Formation modeling is used to model the locations of the boundaries between subsurface layers and layers properties in a subsurface formation in close proximity to a wellbore. Formation modeling may be an interactive process whereby a user interacts with a computer model, e.g., through a graphical user interface, to select the locations and properties of subsurface layers in a subsurface formation.
Formation modeling is generally based upon sensor data collected from one or more types of sensors that are placed in a wellbore either during drilling of the wellbore or after drilling, and as such, the data is generally focused in an area in close proximity to the wellbore itself. While some sensors are capable of collecting data that may extend several feet or meters from a wellbore, other sensors collect much shallower data, e.g., within 6 to 24 inches or less around a wellbore. Regardless, the distances within which all such sensors collect data are orders of magnitude smaller than the size of a subsurface formation or even the lengths of the wellbores from which the data is collected, as wellbores may extend thousands of feet or meters below the surface.
Generally, when performing formation modeling, a user is presented with a two or three dimensional view of the wellbore as well as additional depictions of relevant sensor data, and the user interprets that data and selects locations around the wellbore to define points and/or line segments representing boundaries between adjacent subsurface layers. A work zone may be defined around a wellbore to enable a user to interact with a small region around the wellbore. A work zone is generally rectangular in shape, however, and it has been found that particularly for modeling from sensor data that is shallow in nature, formation modeling is complicated by the use of such a rectangular work zone because the work zone may necessarily include regions that are spaced beyond the range of the sensors used to collect the sensor data, and further, because artifacts may be introduced as a result of automated efforts to define the boundaries between adjacent subsurface layers.